Historically, diesel engines, especially heavy duty diesel engines, have utilized 15W-40 multi-grade lubricants and higher viscosity grades. However, the demand for enhanced fuel economy is driving the marketplace to lower viscosity oils. This has led to increases in air entrainment with some engines resulting in “overflow” of the oil and shutdown of the engine. Air entrainment may arise from various mechanical sources, including mechanical flaws such as cracks or leaking parts or seals, or from the crankshaft splashing in oil in the oil pan, particularly if an excess of oil is present.
Antifoam agents are known, and in certain end-use applications (e.g., transmission fluids), mixtures of antifoam agents have been used. For instance, U.S. Pat. No. 6,251,840, Ward et al., Jun. 26, 2001, discloses a lubricating/functional fluid which exhibits in use improved antiwear and antifoaming properties. The improvements are said to result from use of 2,4-dimercapto-1,3,4-thiadiazole and derivatives thereof together with silicone and/or fluorosilicone antifoam agents.